carbonization

A process by which solid residues with increasing content of the element carbon are formed from organic material usually by pyrolysis in an inert atmosphere.

Note:

As with all pyrolytic reactions, carbonization is a complex process in which many reactions take place concurrently such as dehydrogenation, condensation, hydrogen transfer and isomerization. It differs from coalification in that its reaction rate is faster by many orders of magnitude. The final pyrolysis temperature applied controls the degree of carbonization and the residual content of foreign elements, e.g. at
the carbon content of the residue exceeds a mass fraction of 90 wt.%, whereas at
more than 99 wt.% carbon is found.

Source:

PAC, 1995, 67, 473
(Recommended terminology for the description of carbon as a solid (IUPAC Recommendations 1995))
on page 484